Healthcare is essential in welfare of modern society, especially for infants, bedridden patients and elderly persons who need constant life sign monitoring. Such life sign monitoring is currently achieved by regular inspection of care-aid personnel, e.g., babysitters, nurses and/or medical doctors. However, monitoring relied on manual effort suffers from unintentional negligence and/or inexperience, causing interruption for those who need rest, and/or failure to immediately reflect medical emergency because of long inspection periods. Demands on automated and unattended life sign monitoring technology therefore emerge.